With the development of the industrial technology, the battery is applied in more and more fields as a power source. SOC (State of Charge) is a ratio of the remaining capacity of a battery at a certain discharging rate to a rated capacity under the same conditions. A battery management system may calculate the SOC to be displayed to a user. The user may know a charging progress of the battery by viewing the displayed SOC when charging the battery.
Now, an ampere-hour method and an open-circuit voltage method are generally adopted to calculate the SOC. The ampere-hour method calculates the SOC by measuring the capacity that is charged into and discharged from the battery in real time by integral, and keeping recording and monitoring the capacity of the battery for a long time. However, the ampere-hour method does not take the state of the battery into account, which may cause an error between the calculated SOC and the actual SOC. The open-circuit voltage method requires the battery to stand for a long time until the battery reaches a voltage stability state, so as to calculate an accurate SOC. However, in the process of using the open-circuit voltage method to calculate the SOC of the battery, the time for the battery to stand to reach the voltage stability state may not be determined accurately. As a result, the voltage is often calculated when the battery has not reached the voltage stability state yet, and thus there may be a large error between the calculated SOC and the actual SOC. In this case, due to a larger calculated SOC, a phenomenon that the battery cannot be fully charged may occur in the process of battery charge. For example, when the actual SOC is 97% but the calculated SOC is 100%, it is assumed that the battery has been fully charged since the calculated SOC is 100%, and thus the charging of the battery is stopped. But in fact, the battery is not fully charged. On the other hand, due to a smaller calculated SOC, the SOC to be displayed to the user may abruptly change in the process of battery charge. For example, the actual SOC is 99%, but the calculated SOC is 96%. After that, when the actual SOC reaches 100%, the battery may assume that the calculated SOC of the battery is 100%. As a result, the displayed SOC may jump from 96% to 100%.